1. Field of the Invention
This invention relates to carburetor fuel level sensors and to a management system for monitoring fuel level in a carburetor float bowl and maintaining the fuel level at a desired level.
2. Description of the Related Art
In racing applications it is common to monitor various parameters of the vehicle and acquire data for use in tuning the vehicle for maximum performance. For example, in drag racing applications it is common to monitor engine RPM, exhaust temperature for each cylinder, manifold vacuum or pressure, fuel pressure, drive shaft RPM, G-force and suspension travel. These parameters are plotted against time and stored for later download and analysis. In other types of racing, telemetry is used to transmit the data to a remote receiver for contemporaneous analysis.
One engine parameter which is not monitored is the fuel level in the float bowl of the vehicle""s carburetor. (Carburetors are still commonly used for fuel delivery in racing and other high performance applications even though they are no longer commonly used in production automobiles.) Fuel level is critical because the engine will run too rich if the fuel level is too high and too lean if the fuel level is too low. Either condition can drastically effect performance.
Fuel level is statically set to a preferred level by adjusting a float valve at the carburetor inlet and observing the float level through a xe2x80x9ctrickle holexe2x80x9d or sight glass in the carburetor bowl. There is presently, however, no means for monitoring the fuel level during an event to determine if it stays at or near the preferred level, nor is there means for maintaining the fuel level at the preferred level.
U.S. Pat. No. 3,691,824 to Vanderbilt, Jr. et al. discloses a Carburetor Evaluation System having a fuel level sensor probe which comprises a pair of vertically spaced thermistors with a heating coil positioned midway therebetween. The probe is moved up and down a wall of the fuel bowl to determine the fuel level. As the probe is moved, resistance in the thermistors will vary with the temperature of the adjacent portion of the float bowl wall. Because fuel in the bowl will conduct heat away from the float bowl wall, the temperature of the wall will be lower below the fuel level. The resistance of the thermistors will thus be approximately equal when both thermistors are positioned either above the fuel level or below the fuel level. When one thermistor is below the fuel level and the other is above the fuel level, there will be a difference in resistance. The difference in resistance will be greatest when the fuel level is aligned with the heating coil an thus midway between the thermistors. The probe can thus be used to locate the fuel level by moving it up and down until the point of greatest difference in resistance is found.
Because the probe must be moved up and down the fuel bowl wall to locate the fuel level, it is only useful as a test instrument for use on a stationary vehicle or an engine on a test stand. It cannot, however, be used to sense changes in fuel level while a vehicle is in motion. The evaluation system is used solely for data acquisition and is not provided with any means for controlling fuel level in the bowl.
Hideg et al., U.S. Pat. No. 4,526,152, discloses a low pressure fuel injection system having a sealed fuel chamber which is normally full of fuel. Under high temperature conditions, some of the fuel may vaporize, causing the fuel level to drop. A float in the bowl is equipped with a Hall effect head which cooperates with a second head mounted in the top of the bowl to measure changes in fuel level. As the fuel level drops, the two heads move apart. When the level drops too low, a signal is sent to a valve in a fuel return line to vent vapor from the chamber, thereby allowing the fuel level to rise. This system thus employs a fuel level sensor to control fuel level in a fuel chamber, however, the system is neither intended for, nor easily adaptable to carburetor vehicles.
There remains, therefore, a need for a carburetor fuel level sensor which can sense changes in fuel level in a moving vehicle, as well as for a system using such a sensor to maintain fuel level at a desired level.
The present invention comprises a carburetor fuel level management system for an internal combustion engine with a carburetor. The system includes a fuel level sensor connected to the float bowl of the carburetor and providing an indication of actual fuel level in the float bowl. The sensor may, for example, comprise a pair of generally parallel spaced apart conductors mounted in the float bowl and oriented generally vertically. As the fuel level in the float bowl varies from the desired fuel level, electrical resistance and capacitance across the conductors will vary in proportion to the variation in fuel level. A circuit connected to the conductors typically includes a signal conditioner which produces a signal having a voltage which varies in proportion to the changes in resistance or capacitance across the conductors. The signal is transmitted to a computer which reads the signal and makes a determination of actual fuel level the float bowl therefrom.
The system can also be used to maintain fuel level in the float bowl at or near the desired level by selectively varying fuel flow rate through the inlet line into the float bowl and using the fuel level sensor to provide feedback of actual fuel level. For example, if a fuel pressure regulator is mounted in the inlet line, the computer can selectively operate a solenoid valve mounted in a bypass line which bypasses the fuel pressure regulator. When the solenoid valve is open, fuel of higher than normal pressure is directed to the carburetor inlet, causing the fuel level to rise. Alternatively, if an electric fuel pump is used to move fuel through the inlet line, the computer can control the fuel flow rate by varying the supply voltage to the fuel pump.
If the fuel system supplying fuel to the carburetor includes an external bypass for returning excess fuel to the fuel tank, the fuel level management system can be used to selectively open and close a solenoid valve controlling fuel flow through the inlet line in response to feedback from the fuel level sensor. In this application, the fuel level management system performs a function which is analogous to that normally performed by the mechanical float and float valve in the carburetor bowl. The electronic fuel level management system, however, is capable of working at higher fuel pressures than is a mechanical float valve. The system can thus be used in addition to, or in place of, the mechanical float valve.